The invention relates to a, in particular direct, acceleration sensor, an arrangement and a method for detecting a, in particular longitudinal, loss of road grip of a vehicle wheel.
In the context of the present invention, the term vehicle wheel means a rim with a tire, wherein the tire makes contact with the road surface on which the vehicle is moving. In this context, vehicle relates, in particular, to a passenger car. The term “loss of road grip (adhesion)” means that the tire slides or, at least, partially spins. This means that, in case of ideal road grip, the rotational speed of the tire corresponds to the speed of the vehicle on the road surface (*for motor sports purposes, the ideal road grip is at 10-20% slip). A loss of road grip (short term or for a longer period of time) leads to a difference between the rotational speed of the tire and the speed of the vehicle on the road surface.
Indirect acceleration sensors, arithmetic circuits, arrangements and methods for an approximate detection are generally known from prior art. A device (positioned at the dashboard) for monitoring the centrifugal force on the entire vehicle, which occurs when driving through curves, is known from DE 821 562. In this context, neither an acceleration in the driving direction nor the behavior of the individual wheels is determined.
Thus, in particular indirect, acceleration sensors are known for example from DE 198 13 941 A1, DE 199 30 779 A1, US 2009/0071249 A1, DE 10 2009 021 567 A1. Methods for evaluating acceleration sensors arranged at or in a vehicle wheel are known from EP 0 517 082 A2, US 2011/0082663 A1, WO 2005 069 993 A2, DE 102 23 214 A1, DE 11 2011 100 969 T5, DE 10 2007 014 765 A1. US 2009/0071249 A1 describes, in particular, an acceleration sensor arranged inside a tire of a vehicle. In addition, it is described that an acceleration sensor is used to detect a vibration of the tire in the circumferential direction, and that another acceleration sensor is used to detect a vibration in the tire width direction so that a road surface friction coefficient can be determined.
Furthermore, an arithmetic circuit for monitoring the slip at the wheels of vehicles is known from DE 32 06 694 A1. To this end, the respective rotations of the wheel are counted at each wheel and (if there is a respective difference) the acceleration of the wheel is calculated from two subsequent signals. DE 10 2007 052 749 A1 discloses a method for calculation the wheel slip. In this context, the drive torque applied to at least one wheel is changed and the reaction of the wheel (speed) to this change is measured and evaluated. A method for estimating the adhesive friction between the wheel and the road is known from US2005/0033499 A1. Said method includes applying a positive torque on a first axle and a negative torque on the rear axle, through which, amongst others, the adhesive friction coefficient is determined. U.S. Pat. No. 3,744,850 discloses a control system for the wheel traction which automatically determines the wheel slip with the maximum traction and maintains the latter by controlling braking and accelerating. To this end, the quotient of the linear acceleration and the angular acceleration is determined.
Against this background, it is the object of the invention to create an improved, in particular direct, acceleration sensor, an arrangement and a method for detecting a loss of road grip of a vehicle wheel, in particular, for detecting a loss of road grip before the vehicle, in particular the entire vehicle, loses a stable driving behavior.